1 //===- SyncDependenceAnalysis.h - Divergent Branch Dependence -*- C++ -*-===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // \file
10 // This file defines the SyncDependenceAnalysis class, which computes for
11 // every divergent branch the set of phi nodes that the branch will make
12 // divergent.
13 //
14 //===----------------------------------------------------------------------===//
15 
16 #ifndef LLVM_ANALYSIS_SYNC_DEPENDENCE_ANALYSIS_H
17 #define LLVM_ANALYSIS_SYNC_DEPENDENCE_ANALYSIS_H
18 
19 #include "llvm/ADT/DenseMap.h"
20 #include "llvm/ADT/PostOrderIterator.h"
21 #include "llvm/ADT/SmallPtrSet.h"
22 #include "llvm/Analysis/LoopInfo.h"
23 #include <memory>
24 
25 namespace llvm {
26 
27 class BasicBlock;
28 class DominatorTree;
29 class Loop;
30 class PostDominatorTree;
31 
32 using ConstBlockSet = SmallPtrSet<const BasicBlock *, 4>;
33 
34 /// \brief Relates points of divergent control to join points in
35 /// reducible CFGs.
36 ///
37 /// This analysis relates points of divergent control to points of converging
38 /// divergent control. The analysis requires all loops to be reducible.
39 class SyncDependenceAnalysis {
40   void visitSuccessor(const BasicBlock &succBlock, const Loop *termLoop,
41                       const BasicBlock *defBlock);
42 
43 public:
44   bool inRegion(const BasicBlock &BB) const;
45 
46   ~SyncDependenceAnalysis();
47   SyncDependenceAnalysis(const DominatorTree &DT, const PostDominatorTree &PDT,
48                          const LoopInfo &LI);
49 
50   /// \brief Computes divergent join points and loop exits caused by branch
51   /// divergence in \p Term.
52   ///
53   /// The set of blocks which are reachable by disjoint paths from \p Term.
54   /// The set also contains loop exits if there two disjoint paths:
55   /// one from \p Term to the loop exit and another from \p Term to the loop
56   /// header. Those exit blocks are added to the returned set.
57   /// If L is the parent loop of \p Term and an exit of L is in the returned
58   /// set then L is a divergent loop.
59   const ConstBlockSet &join_blocks(const Instruction &Term);
60 
61   /// \brief Computes divergent join points and loop exits (in the surrounding
62   /// loop) caused by the divergent loop exits of\p Loop.
63   ///
64   /// The set of blocks which are reachable by disjoint paths from the
65   /// loop exits of \p Loop.
66   /// This treats the loop as a single node in \p Loop's parent loop.
67   /// The returned set has the same properties as for join_blocks(TermInst&).
68   const ConstBlockSet &join_blocks(const Loop &Loop);
69 
70 private:
71   static ConstBlockSet EmptyBlockSet;
72 
73   ReversePostOrderTraversal<const Function *> FuncRPOT;
74   const DominatorTree &DT;
75   const PostDominatorTree &PDT;
76   const LoopInfo &LI;
77 
78   std::map<const Loop *, std::unique_ptr<ConstBlockSet>> CachedLoopExitJoins;
79   std::map<const Instruction *, std::unique_ptr<ConstBlockSet>>
80       CachedBranchJoins;
81 };
82 
83 } // namespace llvm
84 
85 #endif // LLVM_ANALYSIS_SYNC_DEPENDENCE_ANALYSIS_H
86